1. Field of the Invention
The invention is generally related to the area of liquid flow and dispensing. More particularly, the present invention is related to synchronized flow from two or more volumetric tanks.
2. The Background of Related Art
There are many applications in which various liquids need to be mixed with precise ratios. Dispensing specific amounts of liquids per a rate controls the formulation of a liquid mixture. The process is traditionally achieved through the use of either balance scales or metering pumps. Metering pumps have the additional capability of providing not only a specific amount of liquid, but also a specific flow rate of liquid. However, both of these devices need to be recalibrated periodically in order to keep accuracy. If a balance scale or metering pump was found to be out of calibration, all measurements since the last calibration could be questionable, potentially leading to recalls and remanufacture of suspected products from the balance scale or metering pump.
Gasoline and ethanol are commonly combined in specific ratios as a motor fuel. Variability in the ratio may cause undesirable variation in the properties of the motor fuel. Gasoline and ethanol are not combined until being shipped from a terminal to a local retailer as the ethanol component increases the solubility of impurities from the surrounding environment. A variety of methods are employed to fill tanks with a specific ratio and amount of gasoline and ethanol in a delivery truck.
One method to obtain a specific ratio of two liquids in a common storage tank is to transfer a specific amount of one liquid, and then subsequently transfer a specific amount of another liquid to the same tank. This method is frequently used because no special equipment is required. One of the disadvantages to this method is that the accuracy of the ratio depends on the accuracy of the device(s) that meters the amount of each liquid transferred. Another one of the disadvantages is that if the two liquids are not miscible to a large degree, then the two liquids may remain segregated as two distinct phases in the common tank unless some sort of mixing apparatus is applied.
The above method is commonly used to sequentially transfer ethanol and gasoline to tank trucks at a distribution terminal prior to delivery to motor fuel retailers. This technique is colloquially referred to as “splash blending”, on the assumption that the liquid splashing around in the tank will cause it to mix homogenously. However, the gasoline and ethanol are often not well mixed upon delivery to a storage tank at a retailer, which has potentially serious negative implications for motor vehicles that may not tolerate a motor fuel with too much ethanol.
Still another disadvantage of this method is a possibility of inadvertently beginning the transfer of the two liquids in uncontrolled flows in a receiving tank, causing a blend with the incorrect ratio of the two components. Blending two chemicals with an incorrect ratio could cause an unwanted result.
Alternatively, the two liquids are pumped at controlled flow rates resulting in a desired ratio. This method depends on two separate liquid flow controllers to maintain a sufficient degree of accuracy to achieve the required ratio. The accuracy of liquid flow controllers, like many electronic measuring devices, can drift over time from acceptable levels, and can require periodic calibration and possibly other preventive or corrective maintenance measures. If the calibration has been found to have deviated from acceptable levels, the quality of all mixtures made since the last calibration are now in question.
Therefore, there is a great need for techniques of measuring and controlling both the dispensing of liquid amounts and liquid flow rates thereof, without the need for periodic recalibration.